Welding is an important operation in producing and maintaining the structural integrity of any structure. Welding is a process by which different materials are joined by fusion. Materials heated to a melting point form a molten pool of material that then can cool to form a weld joint. The materials usually used to form a weld include a base material and a type of filler that when melted together form the molten pool. Through such a welding process, the joint can be formed to be as strong as the base material that was used to form the weld.
There are many methods used in modern industries that can create welds. Gas metal arc welding is one such method. During the gas metal arc welding process, an electric arc forms between a consumable wire electrode and the base material. Receiving power from a constant voltage direct current source, the electric arc heats the base material causing the base material to melt along with the wire electrode to form a molten pool. When the molten pool cools a weld is formed. Throughout the welding process shielding gas is used to protect the gas metal arc welding process from airborne contaminants.
One of the more difficult structures to weld or to repair is a structure in which an enclosed box is present. Ideally, a weld operator would like to have access to the back of a weld joint to properly strengthen the weld and place a backing material so that the molten material does not fall into the structure. However, if damage occurs to an enclosed box structure or when manufacturing the final side of an enclosed box structure access to the back side of the weld joint is not always possible. To remedy this, and affix a suitable backing for the molten pool, a steel plate is usually placed inside the box structure and attached to the sides of the weld joint. The weld is then performed filling in the weld joint and fixing the damaged box structure.
Depends on weld joint type, geometry and direction of loading, welds are assigned a fatigue class value to determine the strength of the weld created. The higher the alphabetic value of the fatigue class, the shorter fatigue life of the weld. While such a process is effective in forming a weld, attaching a steel plate to the back of a box structure to be repaired or produced can process weaker welds that may receive a low fatigue class rating of F2 to F. By way of background, it should be noted that when the weld is created in such a method the steel plate used to hold the molten pool actually becomes part of the weld as part of the steel plate melts to become part of the molten pool. This leads to the steel backing plate no longer being flush to the backside of the weld joint and actually attached to the box structure at the back of the weld joint. Such welds can lead to weld failure due to the additional stress incurred at the weld roots by this type of weld.
Additionally, weld repair for boxed structures may involve small weld joints and weld joints that are difficult to access. Because of this it may be difficult to place a steel backing material on the backside of a weld joint to produce a traditional repair weld. French Patent Application FR2308282A7 attempts to solve this limited access problem that exists regarding boxed structures. In FR2308282A7 an upper hook can lower down a steel backing plate and hold it flush against the backside of the weld zone so that the operator can complete the weld needed to repair the sealed box structure. However, this method only produces the lower class welds described above since a steel plate is used to support the back of the weld pool.
Therefore, it would be advantageous to develop a new type of welding apparatus and method in which a user can not only fix or create a weld on an enclosed box structure, but also develop a welding apparatus and method which can additionally create a weld having a stronger fatigue class value thereby improving the strength and operational life of the weld.